1. Field of the Invention
This invention relates to a treating solution applying method for applying a treating solution such as resist to surfaces of substrates such as semiconductor wafers.
2. Description of the Related Art
In a conventional method of applying a treating solution such as resist to a surface of a substrate, the treating solution is supplied adjacent the center of the substrate spinning at high speed in a plane parallel to a principal plane thereof. The treating solution supplied is spread by centrifugal force to cover the entire surface of the substrate. This method, called a spin coating method, has a drawback of consuming a large quantity of resist by the time the entire surface of the substrate is covered by the resist.
Under the circumstances, a different method has been proposed for applying a treating solution over the entire surface of a substrate. In this method, while spinning the substrate, a nozzle that delivers the treating solution from the tip thereof is moved between a position having the tip opposed to the spin center of the substrate and a position having the tip opposed to an edge of the substrate. Such applying method is disclosed in Japanese Patent Publications (Unexamined) Nos. 2000-350955 and 2001-113217, and U.S. Pat. Nos. 6,191,053, 5,094,884 and 5,885,661, for example.
FIG. 20 is an enlarged fragmentary sectional view showing a treating solution 101, 102 applied to a wafer W.
Depending on surface conditions of wafer W, the wafer surface may have poor wettability with resist. Consequently, in the conventional treating solution applying method noted above, repulsion of the resist or treating solution on the surface of wafer W adjacent the spin center and other locations causes an omission or unevenness of the treating solution 101, resulting in voids 103 and 104 as shown in FIG. 20. An additional application of the treating solution in a large quantity as indicated by numeral 102 in FIG. 20 has a certain effect with respect to the omission or unevenness of the treating solution. However, this measure gives rise to a different problem of requiring an excessive quantity of the coating solution.
In a further method proposed heretofore for applying a treating solution to the surface of wafer W, delivery of the treating solution to the surface of wafer W is stopped once and then the wafer W is spun again. This step spreads the treating solution from the center of wafer W radially toward the edges of wafer W, thereby uniforming the thickness of the treating solution over the surface of wafer W. According to this method, even when an omission or unevenness of the solution takes place adjacent the edges of wafer W, the spin of wafer W causes a surplus part of the treating solution present adjacent the center of wafer W to spread radially toward the edges of wafer W. This produces some effect without increasing the overall quantity of the treating solution. However, when voids 104 are caused by omission or unevenness of the solution adjacent the center of wafer W, the spin of wafer W cannot eliminate the omission or unevenness of the solution since there is nothing to compensate for the shortage of the solution adjacent the center of wafer W.
In the conventional treating solution applying methods described above, the omission or unevenness of the solution adjacent the spin center of the substrate is caused also by a discrepancy in the timing of delivery of the treating solution from the nozzle and movement of the nozzle.
The object of this invention, therefore, is to provide a treating solution applying method for applying a treating solution uniformly over the entire surface of a substrate without requiring a large quantity of treating solution.
The above object is fulfilled, according to this invention, by a treating solution applying method comprising a substrate spinning step for spinning a substrate in a plane parallel to a principal plane thereof at a first spinning speed of 100 rpm to 500 rpm, a first applying step for supplying a treating solution to a surface of the substrate by moving a nozzle from a position opposed to an edge of the substrate in a spin toward a position opposed to a spin center of the substrate while delivering the treating solution from the nozzle, a second applying step for supplying the treating solution to the surface of the substrate by stopping the nozzle at the position opposed to the spin center of the substrate in the spin while delivering the treating solution from the nozzle, and a film thickness adjusting step for stopping delivery of the treating solution from the nozzle, and spinning the substrate in the plane parallel to the principal plane thereof at a second spinning speed faster than the first spinning speed.
With this treating solution applying method, the treating solution such as resist may be applied uniformly over the entire surface of the substrate without requiring a large quantity of the solution.
In a preferred embodiment of the invention, the second spinning speed is 1,000 rpm to 3,500 rpm.
In another aspect of the invention, a treating solution applying method comprises a substrate spinning step for spinning a substrate in a plane parallel to a principal plane thereof at a first spinning speed, a first applying step for supplying a treating solution to a surface of the substrate by moving a nozzle from a position opposed to an edge of the substrate in a spin toward a position opposed to a spin center of the substrate while delivering the treating solution from the nozzle, a second applying step for supplying the treating solution to the surface of the substrate by stopping the nozzle at the position opposed to the spin center of the substrate in the spin while delivering the treating solution from the nozzle, a third applying step for supplying the treating solution to the surface of the substrate by moving the nozzle from the position opposed to the spin center of the substrate in the spin toward a position opposed to an edge of the substrate while delivering the treating solution from the nozzle, and a film thickness adjusting step for stopping delivery of the treating solution from the nozzle, and spinning the substrate in the plane parallel to the principal plane thereof at a second spinning speed faster than the first spinning speed.
In the second applying step, the substrate, preferably, is spun at a third spinning speed, e.g. 100 rpm to 300 rpm, slower than the first spinning speed.
Other features and advantages of the invention will be apparent from the following detailed description of the embodiments of the invention.